Experimental evidence for apparent competition in a tropical forest food web

Abstract

The herbivorous insects of tropical forests constitute some of the most diverse communities of living organisms1. For this reason it has been difficult to discover the degree to which these communities are structured, and by what processes. Interspecific competition for resources does occur, but its contemporary importance is limited because most pairs of potentially competing insects feed on different host plants2. An alternative way in which species can interact is through shared natural enemies, a process called apparent competition3. Despite extensive theoretical discussion there are few field demonstrations of apparent competition, and none in hyper-diverse tropical communities. Here, we experimentally removed two species of herbivore from a community of leaf-mining insects in a tropical forest. We predicted that other species that share natural enemies with the two removed species would experience lower parasitism and have higher population densities in treatment compared with control sites. In both cases (on removal of a dipteran and a coleopteran leaf-miner species) we found significantly lower parasitism, and in one case (removal of the dipteran) we found significantly higher abundance a year after the manipulation. Our results suggest that apparent competition may be important in structuring tropical insect communities.

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Figure 1: Quantitative food web17 showing leaf-miner species (bottom bars), parasitoid species (top bars), trophic links among them, and the species predicted to be affected by the manipulation.
Figure 2: Effect of species removal on parasitism (a) and species abundances (b) 1 year after the manipulation.

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Acknowledgements

We are particularly grateful to A. Lord. We thank Ch. Bol, Ce. Bol, I. Bol, N. Coc, L. Davies and E. Saquil for support and assistance in the field, and our taxonomic collaborators, including J. LaSalle, D. Quicke and C. Whitefoord. Research permission was granted by the Ministry of Natural Resources in Belize, and we are grateful to the Natural History Museum London for allowing us to work at Las Cuevas, and the Natural Environment Research Council for financial support. O.T.L. is a Royal Society University Research Fellow.

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Correspondence to Rebecca J. Morris.

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Morris, R., Lewis, O. & Godfray, H. Experimental evidence for apparent competition in a tropical forest food web. Nature 428, 310–313 (2004). https://doi.org/10.1038/nature02394

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